Yellow-legged Gull - Larus michahellis

(last update: October 08 2013)

Coordinators:
Delfín González
Gabriel Martín
Antonio Gutierrez
Amir Ben Dov
Mars Muusse

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Larus michahellis - 1CY July

This website deals with the Yellow-legged Gull taxon michahellis, which is a common migrant from July to December in NW Europe. After extensive expansion of the breeding population during the last three decades, it nowadays can be found breeding in Belgium, the Netherlands and Britain in mixed couples with both Herring Gull (argenteus) and Lesser Black-backed Gull (graellsii). There are subtle differences between the populations from the Mediterranean, Atlantic coast of Portugal and Morocco and from the islands in the Atlantic. Most pronounced differences can be found in the taxon atlantis, now regarded as full species by some authors and birds along the Atlantic coast of the Iberian peninsular: lusitanius. Both atlantis and lusitanius are treated in their own sections on this website.

General description:

Identification of juvenile Yellow-legged Gulls isn't always easy, but with a combination of characteristics, positive identification must be possible in almost all of them. Within the region (NW Europe), most confusion may arise with juvenile Herring Gulls argentatus and argenteus and juvenile Lesser Black-backed Gulls graellsii. Juvenile white-headed gulls from E and SE Europe, e.g. Steppe Gull cachinnans, Baraba Gull barabensis, and Armenian Gull armenicus are other candidates for causing problems, and some of the birds may be best left unidetified.

Yellow-legged Gull michahellis 1CY, July 25 2010, Rosas, Cataluna, Spain. Picture: Chris Gibbins. Close to "the average michahellis": typical upperwing pattern, with only weak paler innerwebs on inner primaries and no pale lozenges on the outerwebs. Most of GC with dark centres. Tail with wedge-shaped band and limited proximal spotting on rectrices is common in Med. michahellis. Overall reddish brown plumage.

Caspian Gull cachinnans 1CY, July 24 2013, Katwijk, the Netherlands. Picture: Mars Muusse. Venetain Blind effect on inner primaries, Most of GC with dark centres. Tail with evenly broad band and proximal spotting on central rectrices. Overall greyish plumage.

Armenian Gull armenicus 1CY, July 22 2011, Maagan Michael, Israel. Picture: Amir Ben Dov. Bird in fresh juvenile plumage, showing upperwing pattern.

Lesser Black-backed Gull graellsii 1CY, July 25 2013, Katwijk, the Netherlands. Picture: Mars Muusse. Dark inner primaries, Most of GC extensively dark. Tail with evenly broad band and much proximal spotting. Overall cold brown plumage with buffish fringes.

Herring Gull argenteus 1CY, July 18 2013, Katwijk, the Netherlands. Picture: Mars Muusse. Pale inner primaries with pale lozenges on outer-webs, Notched 'piano key pattern' on GC. Tail with evenly broad band and proximal spotting. Overall pale notched plumage with pale tips o primaries often conspicious.

Some general clues for identifying michahellis in July

• Rather dark inner primaries compared to argenteus and cachinnans, the window is rather ill-defined (see image 5545), but the inner primaries are not all dark as in most graellsii;

• Normally the tertials show an all dark tertial-centre with a smooth white fringe as in graellsii (see image 5699). The tertials are normally not as obviously notched as in argenteus. Michahellis may show a broad well-defined pale bar between the sub-terminal band and the dark centre (a transversal bar), but some variations of the pattern occurs (see also image 5707);

• Pale under-parts: normally a streaked breast-band contrasts with the white chin and the pale belly (see image 5698). The under-parts in argenteus are overall warm coloured, more yellow-brown. In fresh juvenile graellsii the brown sides of the neck are often connected to the brown ear-coverts and the brown runs from the crown to the breast, forming a larger all brown patch;

• Greater coverts often lack the 'piano' pattern in michahellis; a pattern obvious in argenteus (see image 5699). The outermost greater coverts become gradually darker, with only a thin white fringe running all the way to the base. Nevertheless, in some michahellis the greater covert pattern may resemble that of argenteus. Juvenile cachinnans in July normally still show a fresh broad creamy-white tip to the median coverts, creating what might be called a pale bar at the folded wing, when observed from a distance. Michahellis normally lacks this bar and by July, the median coverts may appear slightly worn at the tips already, especially the innermost medians;

• Under-wings are dark clouded or with a vermiculate pattern, much darker than the average cachinnans;

• Shins are often pale, not contrasting with the rest of the legs (see image 5578); the shins are often dark in graellsii;

• The tail-band is broadest at the centre, becoming smaller at outer tail feathers, so obviously different from the broad dark tail-band commonly seen in graellsii and argenteus (see image 11);

• The upper-parts are not rich yellow-coloured as in argenteus, but rather cold pale brown (see e.g. image 5545), with white fringes and brown centres to the scapulars and coverts. Contrary cachinnans, michahellis normally lacks the neat post stamp fringes in the lower scapulars which may be very obvious in cachinnans. By July, michahellis actively moult upper and upper lower scapulars and the juvenile lower scapulars have abraded fringes (for terms used: see Topography section);

• Moult in the upper-parts starts early in the season in michahellis, as can be seen in many images. Michahellis has early fledglings, consequently has more untidy looking plumage in mid-summer juveniles.

Juvenile michahellis by the end of July

One of the most striking characteristics of 1CY michahellis is it's quick moult. As early as the end of July, many scapulars, mantle feathers and sometimes tertials or  wing-coverts are shed or replaced by post-juvenile feathers. From 26 to 30 July 2001, we described 59 juvenile michahellis at NW France: at Etaples (Le Tourquet) and at Le Portel (Boulogne-sur-Mer: 50.42 N, 1.34 E). All present juveniles were included. Over the period, we may have described (incidentally) the same bird when we visited fixed locations (but we kept those counts separated), and the general conclusions on bird present at this location presented here will stand, supported by the images shown at this page.

The general idea is that michahellis, after leaving the colonies in June or July, quickly starts the post-juvenile moult. The first signs of moult are usually detected in the upper scapulars and mantlefeathers, followed by other parts of the body-feathers and sometimes upperwingcoverts and/or tertials. 

The retained juvenile feathers are normally very fresh or only very slightly abraded. Given this good quality of the feathers during this month, it is not likely that these feathers are replaced for maintaining primary plumage functions (i.e. protective and locomotoric) at the moment of renewal. It is likely that the post-juvenile moult has been initiated in order to optimize primary plumage functions during winter.   

Tables

 The small survey in the period July 26-30 2001, showed only one single bird in complete juvenile plumage, i.e. not actively moulting scapulars and mantle. The conclusion is that the vast majority (> 90%) moult scapulars by the end of July and over 25% moult wing-coverts. Only a few (< 5%) had shed tertials.

In the same period a large gull resting place was visited near Venice, Italy. Out of 51 juvenile michahellis, only 1 didn't start moulting mantle feathers, 3 out of 51 didn't start moulting scapulars. These figures are perfectly in line with the survey from NW France. Regarding the moult in the coverts and tertials, birds in Italy are slightly ahead of the birds in NW France.